Conventional electrolytic cells for the extraction of aluminum from alumina comprise a carbon anode immersed in a bath of molten alumina, cryolite and sodium fluoride which is contained in a pot shell lined with a carbon cathode. In use, the cathode portion of the pot becomes spent, i.e. its conductivity sufficiently reduced or its physical integrity compromised so that the pot must be emptied, the carbon cathode lining removed and a new cathode rammed into place in the pot shell.
The spent cathode which is removed in this operation contains carbon and alumina which have until now generally been discarded because there was no good way to separate these two useful components for recycling into the reduction process.
It thus has been the aim for a number of years to develop a commercial process which would permit recovery of the carbon and alumina for recycling in the reduction process.
U.S. Pat. No. 780,297 to Krom et al describes a process for obtaining carbon from Wallastonite ores which contain significant amounts of silica wherein the ore is treated with sulfuric acid enabling silica to occur as relatively fine particles as compared with the graphite particles present in the ore. The two fractions thus produced are then separated by screening. There is no suggestion in this patent that a similar technique would be useful for the recovery of carbon and alumina from spent electrolytic cell linings.